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Over the last 40 years, several empirical correlations have been developed to estimate heat fluxes from the combustion chambers of internal combustion engines. Some of these expressions are based on correlations to compute the Nusselt number for forced convection in turbulent flow inside circular tubes. The fundamental suitability of this kind of empirical model in representing the highly complex processes of in-cylinder heat transfer is questionable, but in practice the models have steadily improved owing to contributions from numerous investigators. Other correlations have a less theoretical basis than those of the Nusselt number form. Formulae of this type have been obtained from the application of simple statistical techniques to large datasets, taking into account several engine operational parameters and engine types. The resulting correlations provide reasonable estimates but perform poorly when extrapolated or applied to novel concepts. In this paper, the most important correlations are reviewed against the features of a modern diesel engine, and research requirements for future modelling developments are identified and discussed.

A detailed programme of work has been undertaken to quantify the suitability of predictive methods for accurate determination of the levels of boiling heat transfer within an internal combustion (IC) engine cooling gallery simulator. An extensive array of experimental data has been obtained as the basis for the predictive validation. Working on the principle of superposition, the convective component of heat transfer has been represented by the established Dittus-Boelter correlation which has been extensively modified to account for developing boundary layers, surface roughness and nearwall viscous effects. The boiling component has been represented by the Chen model, modified for binary fluids and subcooling. For the IC engine cooling application it is concluded that the application of the Chen approach must be complemented by a convective heat transfer model that accurately represents the complex thermo-fluid situation being experienced within a developing flow.

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